A study of the influence of aging on the secretory antibody response in the mouse respiratory system is proposed. Inbred mice (BALB/c x C57BL/6) Fl at three stages of aging, i. e. young adult (16 weeks old), middle-aged (65 week old) and aged (100 weeks old) will be immunized with tetanus toxoid, influenza virus or purified pneumococcal polysaccharide via respiratory route. The immunization will be repeated 21 days after the first stimulation. A portion of mice will be exsanguinated periodically, and upper and lower respiratory secretion as well as serum will be collected for 70 days after the primary immunization. Antibodies will be quantitated by an indirect hemagglutination test, radial diffusion test, and/or radioimmunoassay. The results will be analyzed statistically in terms of the effect of aging on the secretory immune response. The proposed study will help clarify any alteration of the secretory immune mechanism with age as well as investigate possible reasons for the poor recovery of the elderly from common respiratory infections.